This invention relates generally to turbomachines and, more particularly, to vane structures for turbines.
The invention herein described was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force.
In preforming the function of directing the high velocity gases toward a turbine blade at the proper angle, the stationary nozzle guide vane is exposed to very high temperatures and pressures. In order to react against these pressures, the turbine nozzle, or segments thereof, are normally secured to the support structure by way of flanges extending radially from the outer or inner band, with the flanges being bolted to the support structure to render a relatively rigid combination. Due to the high temperature gases, it is then necessary to cool the nozzle segments by way of bleed air from the compressor or the like. In order to increase the efficiency of a turbine, it is desirable to increase the temperature of the gases flowing therethrough. Accordingly, manufacturers of turbomachines are continuously striving for the development of materials which can withstand this environment of higher pressures and temperatures, and simultaneously to improve the methods of cooling such structures.
In the development of high temperature materials such as ceramics and oxide-dispersion-strengthened(ODS) material, the advantages of allowable higher temperatures are somewhat offset by the lower strength of the material. Nozzles made from the lower strength materials are precluded from the use of flanges because of the excessive bending stress which they are not capable of sustaining. Accordingly, segments made from these materials must be fixed within the stationary structure by means other than bolted flanges. Further, the mounting means must provide for a substantially even load distribution, for the differential thermal growth of associated components, and for the freedom of constraints from adjacent components which may prevent the nozzle segment from loading properly against its support structure so as to provide a seal against cooling air leakage into the flow path.
The importance of providing for the use of high melting point, and hence low strength, alloys, becomes more obvious when considering the reduction in engine efficiency with the increased use of cooling air. In other words, if greater amounts of cooling air are required with increased temperature levels in the turbine, then the required bleed air from the compressor represents a corresponding decrease in the overall efficiency of the engine. Accordingly, it is desirable to reduce the amount of turbine cooling air to a minimum.
It is therefore an object of the present invention to provide a turbine nozzle configuration which allows the use of high temperature, low strength materials.
Another object of the present invention is the provision in a turbine nozzle configuration for reducing the bending stresses in the bands and vanes.
Yet another object of the invention is the provision for a turbine nozzle configuration which is supported in a surrounding structure without the use of flanges.
Still another object of this invention is the provision for a turbine nozzle segment configuration which imposes a substantially even load distribution against its support structure to thereby effectively seal against cooling air leakage.
A further object of the present invention is to provide a turbine nozzle configuration which requires a minimum amount of cooling air.
Yet another object of the present invention is the provision of a turbine nozzle configuration which is simple in construction, economical to manufacture, and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.